Download Red Giant Branch

MASS LOSS IN EVOLUTIONARY
MODELS OF LOW AND
INTERMEDIATEMASS STARS
Paola Marigo
Department of Physics and Astronomy G. Galilei
University of Padova, Italy
OUTLINE
 Mass loss on the Red Giant Branch
 old and new formalisms
 old and new methods to probe RGB mass loss
 predicted metallicity dependence
 dust formation
 Mass loss on the Asymptotic Giant Branch
 many different available formalisms
 impact on evolutionary properties (lifetimes, nucleosynthesis, final masses)
 a global calibration method based on EPS models of galaxies
MASS LOSS ACROSS THE H-R DIAGRAM
Mass loss measurements across the H-R diagram (Cranmer & Saar 2011, ApJ, 741, 54)
MASS LOSS FROM
LOW- AND INTERMEDIATE- MASS STARS
(0.8 M/M   6-8)
Significant mass loss takes place during
2 evolutionary phases, both along the
Hayashi lines:
I.
In red giants, before the onset of
large-amplitude pulsation.
Typical mass-loss rates are low,
 10-8 Mʘ/yr .
Where: on the Red Giant Branch and
Early AGB
Main form of mass loss in the lowest
mass evolved stars, i.e. globular cluster
stars.
II. In TP-AGB stars after the onset of
large amplitude pulsation (Mira).
Typical mass-loss rates are large,
up to 10-4 Mʘ/yr (super-winds) .
MASS LOSS ON THE RGB
WHICH IS THE DRIVING MECHANISM?
Dissipation of mechanical energy generated in the convection zone?
Acoustic or magnetic waves? (Fusi Pecci & Renzini 1975)
No definitive theoretical model yet.
Usual recipe: Reimers’ Law for mass loss (Reimers (1975)
Basic assumption: the rate of gravitational energy carried out in the wind
is proportional to the stellar luminosity (dimensional scale argument)
No physical interpretation of the wind mechanism
𝑑𝑀 𝐺𝑀
𝑑𝑀
𝐿𝑅
∝𝐿⇒
=𝜂
𝑑𝑡 𝑅
𝑑𝑡
𝑀
adjustable parameter 0.350.45
A MODIFIED REIMERS' LAW
BASED ON A PHYSICAL APPROACH
( S C H R Ö D E R & C U N T Z 2 0 0 5 , 2 0 07 )
Wind energy balance
Mechanical luminosity
Chromospheric radius
=
From modelling of mechanical energy flux:
convective turbulence => magnetic+acoustic
waves
A RECENT THEORETICAL APPROACH
( C R A N M E R  S A A R 2 01 1 )
Cold Alfvén waves
Hot coronae
Wind models for cool MS and evolved giants based on
magnetohydrodynamic turbolence in the convective
subsurface zones.
GK dwarfs: winds driven by gas pressure from hot coronae
Red giants: winds driven by Alfvén wave pressure
FA*= Alfvén wave energy
f*= filling factor
Schröder & Cuntz (2005) assume dM/dt  FA*
WHAT ARE THE HINTS FOR MASS
LOSS ON THE RGB?
CCG M
Classical inference (Renzini & Fusi Pecci 1988)
 Typical globular cluster turnoff mass is
0.85 M⊙.
Masses of RR Lyrae stars (on the
Horizontal Branch, following He core
ignition at the tip of the First Giant
Branch) are 0.65 M⊙ (from pulsation
theory).
Hence, ~0.20 M⊙ is lost between the
main-sequence and the Horizontal
Branch.
 ~0.20 M⊙ is the mass that should be
lost to account for the morphology
of the extended blue Horizontal Branches
in the HR diagrams of GGCs.
MULTIPLE POPULATIONS IN CCGS AND
HELIUM CONTENT
NGC 2808 (Z=0.0014, age=10.1 Gyr)
Several authors have recently suggested that
multiple populations with widely varying levels of
He abundance may be present in GCs.
The extended blue HB may be explained with
high He content.
This fact would weaken the RGB mass-loss
calibration method based on the HB morphology.
Lee et al. (2005, ApJ, 621, L57)
PULSATION MODELS FOR 47 TUC VARIABLES:
INFERENCE OF MASS LOSS
From theoretical PMR relations
Lebzelter  Wood (2005) concluded
that observations of  Tuc variables are
recovered invoking mass loss operating
on the RGB (Reimers Law) and AGB.
A total amount of . M ejected mass
is required.
DO CURRENT RGB PRESCRIPTIONS
OVERESTIMATE MASS LOSS
Mass loss rates of RGB and AGB stars
in GGCs (M, M, M)
from chromospheric models of the H line
Mass loss increases with L and with
decreasing TEFF
Suggestion of metallicity dependence
Rates are ~order magnitude less than
‘Reimers’ and IR results
Meszaros et al. 2009
ASTEROSEISMOLOGY:
INTEGRATED RGB MASS LOSS
Miglio et al. 2012, MNRAS, 419, 2077
Independent constraints on masses and radii of RGB stars from Kepler data
Solarlike oscillation spectra:
frequency spacing
frequency of maximum power
NGC 6791: a metalrich old open cluster with
FeH and age Gyr
 Red Giant Branch stars
 Red Clump stars
   
      
PREDICTED METALLICIT Y DEPENDENCE
ON THE RGB
age Gyr
all nomalized to  at
FeH
Big spread at increasing Z!
Asteroseismologic estimate
at age  Gyr
Kalirai J S , Richer H B Phil. Trans. R. Soc. A 2010;368:755-782
DUST OR NOT DUST ON THE RGB
A WORD FROM THEORY
In between the observational debate of Origlia et al. 2010 vs Boyer et al. 2010
(see also Momany et al. 2012, Groenewegen 2012)
a strong theoretical conclusion by Gail et al. 2009, ApJ, 698, 1033
Fraction of the element Si condensed into forsterite
grains on the tip of the RGB, with maximum possible
growth coefficient.
Unfavorable conditions of RGB winds:
transition to a highly supersonic outflow
occurs close to the star where temperatures
are too high for dust formation.
Condensation factor very low for all initial
masses and metallicities, except perhaps
for stars of   and  
THE TP-AGB PHASE
Dusty circumstellar envelope
atmosphere
convective envelope
energy sources and
nucleosynthesis
PULSATION: A KEY INGREDIENT
A very rapid rise in Mdot with P to “superwind” values.
Then a very slow increase.
No information on any mass dependence; large variation at a given P.
Based on CO microwave observations
in the wind outflow (Vassiliadis & Wood 1993)
Derived by fitting dust envelope models to the
combined Spitzer 5-35 micron spectra and
simultaneous JHLK photometry
(Groenewegen et al. 2007).
THE ONSET OF THE SUPER WIND:
A CRITICAL ISSUE
The luminosity of termination of AGB evolution (complete envelope ejection) is
determined by the period (luminosity) at which Mdot rises rapidly to "superwind" values.
Theory: The transition to a superwind is dictated by
large amplitude pulsation + dust + radiation pressure (large L)
Observations:
The dust-enshrouded AGB stars
are all large amplitude pulsators.
MASS-LOSS RECIPES
empirical
theoretical
 Vassiliadis & Wood (1993) [empirical, CO microwave estimates
of Mdot, plotted against pulsation period]
 Bowen (1988) and Bowen & Willson (1991) [computed mass
loss rates with simplistic energy loss mechanisms and grain
opacities]
 Blöcker (1995) [formula based on Bowen (1988)]
 Groenewegen (1998) [C star mass loss rates in solar vicinity]
 Wachter et al (2002; 2008) [C star pulsation/mass loss models]
 Groenewegen et al (2007) [C star mass loss rates in the LMC
and SMC from Spitzer observations]
 Van Loon et al. (2005) [O-rich dust-enshrouded AGB and RSG stars in the LMC]
 Mattsson et al. (2010) [C star pulsation/mass loss models]
O-rich models lacking [see Jeong et al. (2003), and S. Hoefner this workshop]
AGB MASS LOSS:
IMPACT ON EVOLUTIONARY MODELS
TP-AGB evolutionary features are dramatically affected by
the adopted mass-loss recipe:
Lifetimes
Determines the number of thermal pulses
Luminosities
AGB tip, HBB over-luminosity of massive
AGB stars
Final masses
Limits the growth of the core mass
Nucleosynthesis
Limits the number and the
efficiency of dredge-up episodes;
affects the HBB nucleosynthesis
COMPARING DIFFERENT MASS-LOSS
FORMALISMS: M I =2.0M ʘ Z I =0.008 Marigo et al. 2012
Vassiliadis & Wood 1993
Vassiliadis & Wood 1993
SW at P=800 days
Bloecker 1995
Wachter et al. 2008
AGB MASS LOSS AND WIND PROPERTIES
Vassiliadis & Wood 1993
Models: Nanni et al. 2012, in prep.
Vassiliadis & Wood 1993 with SW at P=800 days
 Mi=2M
 Mi=3M
 Mi=4M
CHEMICAL YIELDS
Mi.  
Yields relative difference:
C  
other light elements  
Fe group elements up to a factor of 2
Stancliffe  Jeffery 2007, MNRAS, 375, 1280
MASS LOSS AND HOT BOTTOM BURNING
IN A (M I =5 M  Z=0.008) MODEL
Vassiliadis & Wood 1993
Bowen & Willson 1991 + Wachter et al. 2008
Marigo et al. in prep.
NUCLEOSYNTHESIS AND MOLECULAR
CHEMISTRY
Vassiliadis & Wood 1993
Bowen & Willson 1991 + Wachter et al. 2008
Marigo et al. in prep.
AGB MASS LOSS:
CALIBRATING OBSERVABLES
AGB mass loss can be constrained combining accurate evolutionary
models with population synthesis simulations
Lifetimes
Luminosities
test
test
Central star’s mass (WD)
Nucleosynthesis
(3° dredge-up and HBB)
number counts of AGB stars in
star clusters and galaxy fields
luminosity, color, and period
distributions
test
test
initial-final mass relation and
WD mass distribution
M-C transition L in clusters,
C/O values, Li-rich AGB stars
PN abundances
STANDARD CALIBRATORS: AGB STARS
IN MAGELLANIC CLOUDS’ CLUSTERS
 Vassiliadis & Wood 1993
Marigo et al. 2012
STANDARD CALIBRATORS: AGB STARS
IN MAGELLANIC CLOUDS’ CLUSTERS
 Vassiliadis & Wood 1993
 Bloecker 1995
Marigo et al. 2012
STANDARD CALIBRATORS: AGB STARS
IN MAGELLANIC CLOUDS’ CLUSTERS
 Vassiliadis & Wood 1993
 Bloecker 1995
 Bowen & Willson 1991 (C/O<1)
 Wachter et al. 2008 (C/O>1)
Marigo et al. 2012
STANDARD CALIBRATORS: AGB STARS
IN MAGELLANIC CLOUDS’ CLUSTERS
 Vassiliadis & Wood 1993
 Bloecker 1995
 Bowen & Willson 1991 (C/O<1)
 Wachter et al. 2008 (C/O>1)
 Van Loon et al. 2005 (C/O<1)
 Wachter et al. 2008 (C/O>1)
Marigo et al. 2012
STANDARD CALIBRATORS: AGB STARS
IN MAGELLANIC CLOUDS’ CLUSTERS
 Vassiliadis & Wood 1993
 Bloecker 1995
 Bowen & Willson 1991 (C/O<1)
 Wachter et al. 2008 (C/O>1)
 Van Loon et al. 2005 (C/O<1)
 Wachter et al. 2008 (C/O>1)
 Kamath et al 2011 (C/O>1)
VW93 + SW delayed at P=800 days
Marigo et al. 2012
STANDARD CALIBRATORS: AGB STARS
IN MAGELLANIC CLOUDS’ CLUSTERS
 Vassiliadis & Wood 1993
 Bloecker 1995
 Bowen & Willson 1991 (C/O<1)
 Wachter et al. 2008 (C/O>1)
 Van Loon et al. 2005 (C/O<1)
 Wachter et al. 2008 (C/O>1)
 Kamath et al 2011 (C/O>1)
VW93 + SW delayed at P=800 days
 Vassiliadis & Wood 1993 (C/O<1)
 Arndt et al. 1997 (C/O>1)
Marigo et al. 2012
A NEW CALIBRATION APPROACH: ANGST
THE ACS NEARBY GALAXY SURVEY TREASURY
(DALCANTON ET AL. 2009; GIRARDI ET AL. 2010)
High accuracy optical multiband photometry of 62 galaxies
outside the Local Groups (within 4 Mpc).
12 selected galaxies: metal poor [Fe/H]  -1.2
and dominated by old stars, with ages > 3 Gyr
(0.8 M⊙  Mi  1.4 M⊙).
Derivation of SFH from CMD fitting based on Marigo et al.
(2008) isochrones.
AGB STARS IN THE ANGST GALAXIES
RGB and AGB stars detected
Counts of AGB stars brigther than the RGB tip
Typically NAGB 60 - 400 per galaxy
NAGB/NRGB 0.023 – 0.050
Simulations of galaxies: TRILEGAL (Girardi et al.2005)
multi band mock catalogues of resolved stellar populations,
for given distance, SFR, AMR
OBSERVATIONS VS MODELS
Predicted AGB stars
too many
too bright
CURING THE DISCREPANCY:
MORE EFFICIENT MASS LOSS ON THE AGB
AT LOW Z AND OLD AGES
Schroeder & Cuntz 2005
+ Bedjin (1998) like dustdriven mass loss
Shorter TP-AGB lifetimes
Fainter luminosiites
Lower final masses (WDs)
White Dwarf mass measurements in
M4 (Kalirai et al. 2009, ApJ, 705, 408)
before
after
SNAP-11719
(Dalcanton et al. 2011, ApJS, 198, 6)
snapshot survey of 62 galaxies (26 observed)
with the near IR filters WFC3/IR F110W+F160W
SFH from optical CMDs
Complete census of AGB
stars from near IR
SNAP-11719:snapshot survey of 62 galaxies (26 observed)
with the near IR filters WFC3/IR F110W+F160W
(Dalcanton et al. 2011, ApJS, 198, 6)
rCHeB
bCHeB
MS
AGB
RGB
SFH from optical CMDs
Complete census of AGB
stars from near IR
Melbourne et al. 2012, ApJ, 748, 47
RGB + AGB stars responsible for
21% + 17% of the integrated flux
emitted by galaxies in the near IR
Present TP-AGB models show
an average excess:
 50% in the predicted lifetimes,
 factor of 2 in the emitted flux
ODD!
Models are calibrated on direct counts
of AGB stars in MC clusters.
Possible relevant impact in EPS
models of galaxies and mass
determination of high-z objects
(Bruzual 2009).
THE INITIALFINAL MASS RELATION:
DEPENDENCE ON MASS-LOSS EFFICIENCY
THE INITIALFINAL MASS RELATION:
THE 3° DREDGE-UP PLAYS A ROLE!
Mc = Mf-Mc,1tp
a lower limit to the effective
nuclear fuel burnt (hence lifetime)
during the TP-AGB.
Present models of intermediate mass AGB
stars predict a very efficient 3° dredge-up
(), with practically no growth of Mc
(Karakas et al. 2010, Stancliffe et al. 2009).
THE INITIALFINAL MASS RELATION:
DEPENDENCE ON METALLICIT Y
Marigo  Girardi 2007
Non monotonic trend with Z
Karakas 2010
Monotonic trend with Z
CONCLUDING REMARKS
 RGB mass loss
 The classical methodology (Reimers law + HB morphology in GGCs) is currently
debated due to
 Alternative, more physically sound, mass-loss prescriptions
 new scenario of GGCs: multiple stellar populations and He content
 new observational/theoretical techniques (asteroseismology, pulsation
models, infrared data)
 From theory: tiny, if not any, amount of dust on the RGB at subsolar Z
 AGB mass loss
 Onset of the superwind, a critical point still uncertain (M, Z, C/O, L, Teff, P)
 Evolutionary properties heavily affected by the adopted mass-loss law
 Initial-final mass relation: mass loss and third dredge-up both concur to shape it.
 Calibration needed! Population synthesis of AGB stars in clusters and
in fields of galaxies, covering a large range of ages and metallicities.
Ongoing work.